中国典型陆地生态系统水分利用效率及其对气候的响应

水分利用效率(Water Use Efficiency,WUE)是陆地生态系统碳-水耦合的重要指标之一,也是研究陆地生态系统响应全球变化的重要参数。深入了解生态系统WUE的长时序变化特征及其影响因素,对生态系统碳水循环研究以及水资源合理开发具有重要意义。该研究基于2003—2010年中国8个碳通量观测站的通量数据、气象数据分析WUE的年内、年际变化特征及其与关键气候因子之间的响应关系。研究表明:1)处于热带季风气候区的千烟洲、西双版纳、鼎湖山3个站点的WUE全年波动较大,无明显规律,其余5个站点的WUE则表现出明显的季节变化特征,均表现为在4—7月份之间,呈现显著增加的特征,在7—8月份达到最高值,8—10月份,WUE逐渐下降,在11月至次年2月份,植被WUE接近于0;2)2003—2010年间,高寒草甸(当雄)年均WUE值最低(0.18 g/kg),热带雨林(西双版纳)最高(4.20 g/kg)。人工针叶林(千烟洲)、热带雨林(西双版纳)、落叶阔叶林和针叶混合林(长白山)植被WUE呈下降趋势,其余5个生态系统年均WUE呈增加趋势;3)8 d时间尺度上,高寒草甸、农田、草原生态系统WUE分别与气温呈正相关;森林生态系统WUE与气温呈负相关,其中人工针叶林生态系统WUE与气温的负相关系数(r=-0.607,P0.01)明显高于常绿阔叶林和针阔混交林;相比森林和农田生态系统,高寒草甸、草原生态系统WUE与相对湿度和降水具有较高的相关性;4)森林生态系统可通过土壤管理调控、冠层修剪等方式提高水分利用效率;农田生态系统需从灌溉方式、作物育种方面提高水分利用效率;高寒草甸及草原生态系统需采取人工种草、休牧以及划区轮牧等方式增强草原碳汇,从而提高水分利用效率。

Characteristics of water use efficiency of typical terrestrial ecosystems in China and its response to climate factors

Abstract: Water Use Efficiency (WUE) refers to the ratio of water used in plant metabolism over water lost in evapotranspiration, indicating carbon-water coupling in terrestrial ecosystem and its response to global change. It is of great significance to clarify the long-term variation characteristics and influencing factors of WUE for the study of carbon and water cycles and the rational utilization of water resources. This study aims to estimate the vegetation WUE of a research site, particularly on the annual and interannual variation characteristics of WUE, and to establish the response relationship between WUE and key meteorological factors. The data used in this paper mainly include the flux and meteorological information from eight sites in China from January 2003 to December 2010. Unified quality control and interpolation methods were then used to pre-process the flux data. The daily flux and meteorological data were combined into 8-day data sets in each site. Pearson coefficient was used to analyze the correlation between vegetation WUE and Gross Primary Productivity (GPP), ET, average temperature, precipitation, and relative humidity factors. The characteristics and influencing factors of WUE were analyzed and compared in different ecosystem. The results showed that: 1)WUE fluctuated greatly in the whole year without obvious regularity in Qianyanzhou, Xishuangbanna and Dinghushan sites which locate in the tropical monsoon climate region, while WUE showed obvious seasonal variation characteristics in the other five sites, all of which increased significantly from April to July, and reached the maximum during the peak period (July to August), and then WUE decreased gradually from August to October. From November to February of the following year, WUE reached zero. 2) From 2003 to 2010, the annual WUE of alpine meadow (Damxung) was the lowest (0.18 g/kg), whereas, that of tropical rainforest (Xishuangbanna) was the highest (4.20 g/kg). The WUE increased annually in the grassland (Inner Mongolia), broad-leaved evergreen forest (Dinghu Mountain), farmland (Yucheng), alpine meadow (Damxung), and alpine meadow (Haibei), whereas, the decreasing trend occurred in the coniferous forest (Qianyanzhou), tropical rainforest (Xishuangbanna), deciduous broad-leaved and coniferous mixed forests (Changbai Mountain). 3) In the 8-day time scale, there was positively correlation between temperature and WUE in alpine meadow, farmland and grassland ecosystem, whereas there was the negatively correlation between temperature and WUE in forest ecosystem. And the negative correlation between WUE and temperature in coniferous forest ecosystem (R=-0.607, P<0.01) was higher than that in evergreen broad-leaved forest and coniferous broad-leaved mixed forest ecosystem. Compared with forest and farmland ecosystem, WUE in alpine meadow and grassland ecosystem had a higher correlation with relative humidity and precipitation; 4) In different ecosystem, the various approaches were proposed to enhance WUE of terrestrial ecosystem for the sustainable development of agriculture, forestry and animal husbandry. Soil management regulation and canopy pruning can improve water use efficiency in the case of forest ecosystem. In farmland ecosystem, water use efficiency can be elevated from irrigation mode and crop breeding. In alpine meadow and grassland ecosystem, man-made grass, rest grazing and area rotation grazing can be used to enhance grassland carbon sink, further to improve water use efficiency. The findings can provide promising potentials to alleviate water shortage against the background of global warming.